The present invention is directed, in general, to a SAW identification tag reader and, more specifically, to a reader for use with surface acoustic wave (SAW) identification tags having enhanced data content and to methods of operating and manufacturing the same.
Familiar to all are the bar codes and magnetic strips employed by businesses to perform identification functions and the various devices used to read them. Generally, magnetic strips are read by swiping a card with the strip on it, such as a credit card, through a reader. Magnetic strips can also read by contact or proximity devices where the card, such as a parking or access card, is placed on or held close to the reader. Bar codes are most generally read by using a xe2x80x9clight gunxe2x80x9d to read the code and identify the item associated with that particular code. The main reason bar codes and magnetic strips are the identification systems of choice is that they are very cheap.
The applications for which bar codes and magnetic strips are useful is limited, however, by the relatively small amount of data they can encode and their inherent readability limitations. One such readability limitation is the range at which they can be used. Both are short range systems that require the reader to contact or be very close (a few centimeters, at most) to the bar code or magnetic strip, as the case may be, in order to decode data. They are also limited by the fact that no obstruction can be between the reader and the bar code or magnetic strip for the reader to accurately decode data. The orientation of the reader relative to the bar code or magnetic strip can also be a significant readability problem. If the reading device is not properly aligned or is held at an incorrect angle, the encoded information can not be read. As a result of these problems, each individual read operation requires manual scanning by a human operator if high read accuracy is needed. The various limitations of bar codes and magnetic strips have prevented their use in a wide range of applications for machine readable tags that need highly reliable and totally automated reading at read ranges up to several meters.
The radio frequency identification (xe2x80x9cRFIDxe2x80x9d) tag is another prior art identification device. As the name suggests, when RFID tags are interrogated they reflect or retransmit a radio signal that returns encoded identification information. RFID tags have many uses, ranging from the collection of highway and bridge tolls to being embedding in objects to circumvent counterfeiters. An advantage of RFID tags over magnetic devices and bar codes is that they can generally be sensed at a somewhat longer distance without having as significant line-of-sight and orientation problems that are evidenced in bar code and magnetic strip systems. Although RFID tags have a longer reliable range than the ubiquitous magnetic strip and bar code systems, the range at which they can reliably operate is still a limiting factor.
Prior art RFID tag devices are of two basic types; those that contain a microchip and those that do not. There is a radical difference in cost and performance between the two types; to such an extent that they rarely compete with one another as to type of use. As a general rule, chip tags cost more by have a larger data capacity than chipless tags. Chip tags, for example, are usually not available below a unit cost of about one dollar each when ordered in a quantity of less than one million; whereas many chipless tags are projected to cost less than 20 cents each, even when ordered in quantities of one hundred thousand.
Chip tags are by far the most popular. A chip tag consists of four elements or features: (1) a computer microchip; (2) circuits for converting radio signals to computer data signals and back to radio signals; (3) an antenna; and (4) a means for providing DC power to the chip circuitry. In low cost RFID chip tags, the first two features are often partially or totally integrated into a single microchip, which integration requires certain compromises in tag performance (read range, number of bits, etc.). This combination of features also leads to certain integrated circuit (IC) cost and/or design compromises to accommodate both digital and radio frequency circuitry on a single IC. The impact of these design compromises can be partially compensated for by use of low radio frequency (RF) operating frequencies that, in turn, lead to rather large and expensive antennas.
The most daunting problem with chip tags is the need for DC power for the chip circuitry. The combination of environmental issues coupled with severe constraints on cost, size and weight usually requires that the tag not have a battery or other on-board power source. The only generally useable solution is to obtain DC power by converting RF power received from the tag reader signal into DC power within the tag. Those skilled in the pertinent art term tags without a battery or other power source as xe2x80x9cpassivexe2x80x9d tags, while those that contain a battery or other source are termed as xe2x80x9cactivexe2x80x9d tags. The passive method of providing DC power to a chip tag requires a more efficient tag antenna (i.e., larger size and cost) and higher transmitted power levels from the reader. It also requires added components which will either add to the cost of the microchip or to the cost of the tag for the required extra electrical components in the tag, which additional components will also result in an increased tag size. The most important limitation of passive powered chip tags, however, is the severe restriction on the read range of the tag because a signal that is sufficiently strong to power the tag only extends a short distance from the tag reader antenna. Thus, while chip tags have the dominate share of the RFID market, the high cost and limited read range combine to prevent chip tags from replacing either bar codes or magnetic strips in any significant manner.
xe2x80x9cChiplessxe2x80x9d RFID tags do not contain a microchip but, instead, rely on magnetic materials or transistorless thin film circuits to store data. A major advantage of chipless RFID tags is their relatively low cost. The disadvantages of chipless tags include that they are range limited (several centimeters at the most) and only contain limited amounts of information. The severity of these problems has prevented their market acceptance in spite of their low cost potential.
In the year 2000, the current global market for conventional RFID systems and services is in the order of 500 million U.S. dollars. This market is largely for chip tags that typically cost from about one dollar to tens of dollars each. While chipless tags are not selling well, they have generated great interest from a number of potential users because of their low cost potential. A huge gap exists in the automatic identification market between the very low cost bar codes and the higher performing RFID chip tags. The overall market is clamoring for a technical solution to fill that gap. The critical characteristics of the new automatic identification technology to fill this gap are: (1) a cost of between one cent and ten cents per tag when manufactured in high quantities; (2) reliable reading without the need for manual scanning by a human operator; (3) reliable reading without a line of sight between the tag and tag reader (i.e., reliable reading even if the tag is scratched, or covered with dirt, or on the wrong side of the package, etc.); (4) a reliable read range of at least one to two meters; and (5) a tag data capacity of roughly 100 bits. Such tags are of vital interest to postal authorities, airlines and airports, mass transit authorities, animal breeders, the livestock industry, delivery businesses, any business with significant supply chains, particularly those that maintain inventory or handle fast moving consumer goods, and so on. These are all applications where a high priced tag is not practicable, particularly where the tag is disposable or is going to be sold with the product.
To address and overcome the limitations of cost, data capacity and reliable range inherent in prior art RFID tags, a new type of RFID tag has been developed. These tags are the SAW identification tags that are described in detail in U.S. patent application Ser. No. 10/024,624, entitled xe2x80x9cSurface Acoustic Wave Identification Tag Having Enhanced Data Content and Methods of Operation and Manufacture Thereof,xe2x80x9d by Hartmann, commonly assigned with the invention and incorporated herein by reference. In order for the SAW identification tags described by Hartmann to be of use, however, it is essential that a reliable reader capable of sending an interrogation signal and receiving and decoded a reply signal be provided for use with such tags.
Accordingly, what is needed in the art is a SAW identification tag reader that can reliably interrogate a SAW identification tag with substantial data encoded thereon and that can reliably detect and decode such tag""s return signal.
To address the above-discussed deficiencies of the prior art, the present invention provides for a SAW identification tag reader and for methods of operating and manufacturing the same. In one embodiment, the SAW identification tag reader includes: (1) a transmitter capable of sending an interrogation signal that excites a SAW transducer located on a piezoelectric substrate, the piezoelectric substrate having a group of slots arranged by both pulse position and phase position, and a number of reflectors distributed among the slots such that the reflectors return to the transducer a return signal containing a number encoded by both pulse position and phase position; and (2) a receiver for detecting the return signal and decoding the number.
The present invention thus introduces a reader for use with SAW identification tags where the SAW identification tag is constructed to use both phase positions and pulse positions to return an encoded number. By using both phase position and pulse position encoding methods a dramatic increase in the amount of data that a SAW identification tag can contain is achievable. Such increase permits a SAW identification tag to contain a globally unique number, thus permitting the use of such tags for uniquely and reliably identifying and tracking a heretofore unprecedented number of objects. The present invention provides a reader to reliably interrogate such SAW identification tags and accurately decode a number encoded in the return signal under a variety of different environmental conditions.
In one embodiment of the present invention, the reader is used to transmit interrogation signals to, and detect and decode return signals from, a SAW identification tag where reflectors are arranged such that said phase position is in quadrature. In another embodiment, a framing reflector is located between the SAW transducer and the group.
In one embodiment of the present invention, the SAW identification tag reader can read a SAW identification tag that encodes a number that is at least eight bits long. Another embodiment provides for a SAW identification tag reader for use with SAW identification tags that have a plurality of groups separated by dead spaces. In still another embodiment, the SAW identification tag reader can read a SAW identification tag that has at least four groups and encodes a number that is at least 32 bits long. In yet another embodiment, the SAW identification tag reader can read a SAW identification tag that has at least twelve groups and encodes a number that is at least 64 bits long.
A particularly useful embodiment provides for a SAW identification tag reader that uses an interrogation signal that has a frequency of between two and three gigahertz. A particularly advantageous application of this embodiment provides for a 2.45 gigahertz frequency.
A most useful embodiment of the SAW identification tag reader provides for reading a SAW identification tag containing data pertaining to an object associated with the number. This feature permits groups of numbers to be uniquely associated with specific kinds of objects. For example, a certain predetermined block of SAW identification tag numbers can be associated with beef cattle while another block can be associated with automobile parts.
The utility of the SAW identification tag reader is enhanced by an embodiment of the invention that is further comprised of having a computer associated with it. Another aspect of the invention is further comprised of having the SAW identification tag associated with a computer network.
The present invention encompasses a wide array of SAW identification tag reader embodiments. In an embodiment to be illustrated and described, the SAW identification tag reader is selected from the group consisting of a side panel reader, a shelf reader, a doorway reader, a roadway reader, a short range hand-held reader, a long range hand-held reader, a long range fixed reader, a wand reader and a fingertip reader.
The foregoing has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.